1. Field of the Invention
The invention relates to a rotary electric machine
2. Description of the Related Art
Some rotary electric machines include a so-called magnet embedded rotor in which permanent magnets are fixedly embedded in a rotor core, as described in, for example, Japanese Patent Application Publication No. 2010-233346 (JP 2010-233346 A). In such a rotary electric machine, the amount of magnetic flux generated by the permanent magnets is usually substantially constant, and thus the amount of magnetic flux of the rotor is also substantially constant. Thus, the induced voltage (counter electromotive voltage) generated at coils of a stator increases in proportion to the rotational speed of the rotor. When the induced voltage reaches the upper limit of power-supply voltage, it is no longer possible to further increase the rotational speed of the rotor. Therefore, a rotary electric machine may be designed such that the amount of magnetic flux of the rotor is suppressed to an amount at which the rotor is able to rotate at a sufficiently high speed. However, in this case, it is not possible to obtain sufficiently high torque in a low-speed rotation range.
In recent years, there has been proposed a rotary electric machine that is able to rotate at high speed and output high torque in the low-speed rotation range by varying the amount of magnetic flux of a rotor, as described in, for example, Japanese Patent No. 4225001. The rotary electric machine described in Japanese Patent No. 4225001 includes: a rotor having an inner rotor that holds first permanent magnets and an outer rotor that is located radially outward of the inner rotor and that holds multiple pairs of second permanent magnets; and a rotor phase control mechanism that changes the phase (rotation angle) of the outer rotor relative to the inner rotor in the rotational direction. The rotor phase control mechanism controls the phase of the outer rotor to make the polarity of a magnetic pole of each first permanent magnet and the polarity of a rotor magnetic pole that is formed of a pair of second permanent magnets and that is opposed in the radial direction to the magnetic pole of the first permanent magnet opposite to each other, thereby reducing the amount of magnetic flux of the rotor and thus allowing the rotor to rotate at high speed. On the other hand, the rotor phase control mechanism controls the phase of the outer rotor to make the polarity of a magnetic pole of each first permanent magnet and the polarity of a rotor magnetic pole that is formed of a pair of second permanent magnets and that is opposed in the radial direction to the magnetic pole of the first permanent magnet coincide with each other, thereby increasing the amount of magnetic flux of the rotor and thus allowing the rotor to output high torque.
In the rotary electric machine described in Japanese Patent No. 4225001, an oscillating motor, which is used as the rotor phase control mechanism, is incorporated in the rotor, and the phase of the outer rotor is controlled through the operation of the oscillating motor. Therefore, it is inevitable that the configuration of the rotary electric machine becomes complicated. In this regard, there is still room for improvement.